1. Field of the Invention
The present invention pertains to an apparatus and method for noninvasive stimulation of muscles in the upper airway to diagnose and/or treat a breathing disorder, such as obstructive sleep apnea. In particular, the present invention pertains to a magnetic stimulation device and a method of using the device to apply pulsed magnetic fields to the muscles in the neck area of a patient to induce tension in such muscles, thereby relieving the obstructive sleep apnea caused by a relaxation of such muscles. By measuring an awake patient""s compliance in the presence and absence of the magnetic stimulation, the likelihood that the patient suffers from obstructive sleep apnea can be determined.
2. Description of the Related Art
Obstructive sleep apnea (OSA) is a condition in which sleep is repeatedly interrupted by an inability to breathe due to an obstructed upper airway segment. Those afflicted with OSA experience sleep fragmentation and complete or nearly complete cessation of ventilation intermittently during sleep with potentially severe degrees of oxyhemoglobin desaturation. These symptoms may be translated clinically into extreme daytime sleepiness, cardiac arrhythmias, pulmonary-artery hypertension, congestive heart failure and/or cognitive dysfunction. Other consequences of OSA include right ventricular dysfunction, carbon dioxide retention during wakefulness, as well as during sleep, and continuous reduced arterial oxygen tension. Hypersomnolent sleep apnea patients may be at risk for excessive mortality from these factors as well as by an elevated risk for accidents while driving and/or operating potentially dangerous equipment.
Studies of the mechanism of collapse of the airway suggest that during some stages of sleep, there is a general relaxation of the muscles which stabilize the upper airway segment. This general relaxation of the muscles is believed to be a factor contributing to OSA.
Existing therapeutic remedies for treating OSA include the surgical removal of deformed, loose or swollen structures in the upper airway. It is also known to apply positive air pressure at the mouth and/or nose of the patient to xe2x80x9csplintxe2x80x9d the airway, thereby maintaining an open passage to the lungs. In addition, pharmacologic solutions have also been pursued.
Neither of these therapies is successful in all cases. Surgical relief is invasive, introduces a potential for surgical complications and is appropriate in only a small percentage of cases. On the other hand, the nasal mask needed to apply a positive air pressure is not tolerated by some OSA patients. Pharmacological therapy has been, in general, less than satisfactory, and side effects are frequent.
It is also known to treat OSA by electrically stimulating the musculature in the neck area associated with the upper airway. One such method of electrically stimulating the muscles in the upper airway area of a patient involves placing an electrode in direct contact with a surface of the patient and passing a current through the surface tissues of the patient contacting the electrode. For example, an intraoral appliance has been developed that applies electrical currents to the tongue, causing it to contract, thereby helping to clear the airway. Another known appliance applies electrical stimulation to the exterior surface of the patient""s neck below the chin to induce contraction of the upper airway muscles.
Electrical stimulation using surface mounted electrodes creates relatively large current densities at the site of the electrodes. Because these current densities are disposed at the surface of the patient, which also contains a relatively large number of nerve endings, such electrical stimulation devices can cause unpleasant or painful sensations, possibly arousing the user from sleep.
It is also known to apply electrical stimulation to the muscles of the upper airway via electrodes implanted in the patient. Subcutaneous electrodes have the benefit of being positioned adjacent to the muscle or nerve to be stimulated to focus the electrical energy on that muscle/nerve while reducing the amount of collateral tissues effected by the high current densities near the electrode. There are also typically fewer nerve endings deep within the patient than at the surface. Thus, electrical stimulation using implanted electrodes reduces the likelihood that the electrical stimulation will induce an unpleasant or painful sensation in the patient. However, electrical muscle stimulation utilizing implanted electrodes requires surgical intervention, the permanent presence of foreign materials within the patient""s neck tissue, and at least one electrical connection protruding from the patient. Consequently, there is a potential for infection or irritation at the surgical site and at the site where the electrode protrudes through the surface of the patient.
Accordingly, it is an object of the present invention to provide a device for stimulating the muscles in the upper airway area for the treatment of OSA that does not suffer from the disadvantages associated with the above-described conventional OSA treatments. This object is achieved by providing a non-invasive device for magnetically stimulating the muscles that stabilize the upper airway to cause them to contract. Because the stimulation is via magnetic induction, which is capable of stimulation of deep muscular structures, the present invention does not generate large currents at the skin. Therefore, it is less painful than surface electrode electrical stimulation devices.
The muscle stimulator for applying a magnetic field to at least one muscle or muscle group associated with an upper airway in a patient experiencing obstructive sleep apnea to induce tension in that muscle or muscle group to relieve the obstructive sleep apnea includes a plurality of loops of electrical wire and a power supply that selectively provides electrical power to the plurality of loops. Applying power to the loops produces the magnetic field used to stimulate the targeted muscles. A sensor monitors a condition of the patient associated with the obstructive sleep apnea, such as the snoring sounds produced by the patient or the patient""s respiration, to determine when to initiate stimulation and how to change the intensity of the stimulation, if necessary, during the therapy process. A control unit receives signals output by the sensor and controls the application of electrical power from the power supply to the plurality of loops of electrical wire. A positioning appliance secures the plurality of loops of electrical wire to the patient at a position relative to the targeted muscle or muscle group such that the magnetic field produced by applying electrical power to the plurality of loops of electrical wire induces tension in that muscle or muscle group to relieve the obstructive sleep apnea.
It is a further object of the present invention to minimize the heat experienced by the patient as a result of using the magnetic stimulator. To that end, the present invention includes an insulating material between the patient""s skin and the coil. In addition, the temperature of the coil is monitored by a temperature sensor and the power to the coil is controlled based on the temperature of the coil so that excessive heat is not generated in the coil. Also, portions of the coil are maintained as far from the patient as possible while still permitting the magnetic stimulator to provide its therapeutic effect.
It is a still further object of the present invention to control the application of magnetic energy to the patient based on the condition of the patient. To achieve this object, sensors are provided to monitor the condition of the patient. For example, sensors are used to determine whether the patient is snoring and/or experiencing an apneic event. If so, the coil is energized to treat the OSA. Energizing the coil can also be synchronized with the patient""s respiration so that stimulation begins within a predetermined window during the patient""s respiratory cycle, such as at the onset of inspiration or at a period offset therefrom. Also, the present invention contemplates using the conditions of the patient, such as the presence of snoring, an apneic event and/or the respiratory patterns of the patient, to regulate the intensity of the magnetic stimulation. For example, the more prevalent the apneic events, the greater the level of stimulation. Conversely, a reduced number of apneic events results in a reduced level of stimulation. In this manner, only the necessary level of magnetic energy is applied to the patient.
It is a further object of the present invention to provide a method of using the device discussed above to apply a magnetic field to at least one muscle group associated with an upper airway of a patient experiencing obstructive sleep apnea to induce tension in that muscle group to treat the obstructive sleep apnea.
It is yet another object of the present invention to provide a system and method for diagnosing whether a patient is likely to suffer from OSA. This object is achieved by providing a system that measures a compliance of the patient to obtain a first compliance level, applies a magnetic field to at least one muscle group associated with an upper airway of the patient, measures the compliance while applying the magnetic field to obtain a second compliance level, and compares the first compliance level to the second compliance level. The smaller the difference between the first and second compliance levels, the more likely the subject suffers from obstructive sleep apnea.
These and other objects, features and characteristics of the present invention, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention.